Introduction Study Area Helicopters Methodology Results Conclusions Suggestions References Acknowledgements Appendix 1 Appendix 2 Appendix 3 Appendix 4 Appendix 5

Conclusions The intent of this study was to determine the horizontal distance to the 92 dBA (slow) level contour around helicopters as they performed typical helicopter logging operations. We were able to reasonably identify this distance for two helicopters at the log-landing site. The 92 dBA contour for the Kmax and Vertol 107 is about 100 feet and 450 feet, respectively. (These distances are very conservative estimates in that they account for about 97.5 percent of all maximum noise events.) When assessing the impacts of noise during helicopter logging operation, the reader should keep in mind the different payload capacities of the different helicopters and not attempt a simplistic comparison of noise impacts based solely on decibel levels generated. A helicopter with twice the payload capacity of another helicopter could complete logging operations in half the time. As such, an increase in noise per trip could result in an overall reduction in noise impacts. The reader is cautioned not to extrapolate the results of the Kmax and Vertol 107 study to other similar sized helicopters as their acoustic signatures might be very different. The differences in physical features of helicopters, such as engine size and rotor size, can affect the sound levels. Also, the operational differences in the maximum speed of the helicopter rotor or the differences in flexibility of rotors to tilt should be expected to be different enough to produce different sound levels.

Nevertheless, given that the 92 dBA contour for the Kmax and Vertol 107 is about 100 feet and 450 feet, respectively, and that the previously mentioned study by Messingerova and Tajnos (2006) modeled the distance to the 90 dBA as about 160 to 170 feet, it is reasonable to assume that the distance to the 90 (or 92) dBA contour for helicopters during yarding is likely to be only few hundred feet from the source. Some regulators have conservatively estimated that it is necessary to keep helicopter logging operations a mile (some 5,200 feet) from sensitive sources. Based on the results demonstrated in this study, a general restriction of that magnitude appears overkill. Obviously, measurements of at least a few other models of helicopters would help clarify this issue (also see Suggestions for Further Study).